The present invention relates to a milling cutter tool for chip-breaking machining and a cassette intended to be mounted onto said tool, which cassette is placed in a corresponding groove in the milling cutter tool.
In connection with milling cutters comprising mechanically fastened cutting inserts, difficulties have arisen as to the necessary precision at the positioning of the cutting inserts, in order to achieve a fine surface on the workpiece and a long life of the tool. The achievement of the required smooth surface necessitates that the cutting inserts are positioned with greatest possible exactitude, in particular in axial direction. If the axial positioning precision is insufficient, this results in an axial play, which in its turn causes an inferior surface smoothness.
In for instance, the motor industry, close pitch milling cutters are used for milling of cylinder blocks and similar parts. At those applications, very high requirements are set on the surface smoothness and R.sub.a -values of maximally 1.5 .mu.m, R.sub.2 -values of between 10 and 15 .mu.m, R.sub.max -values of 10 .mu.m and WT-values of between 5 and 8 .mu.m are often necessary. In order to at all achieve those surface criteria, it is necessary to position the cutting edges with very high precision, both in absolute terms and relative to the other cutting edges of the milling cutter body. Thus, the axial height difference between two cutting edges may not exceed a few .mu.m. Generally, all cutting edges should lie within an axial tolerance range of 4 .mu.m, and preferrably even less. This has turned out to be practically unattainable for cutting inserts with relatively thick coatings, whose coating thicknesses can vary up to 20 .mu.m. Hence, these differences in the thicknesses of the individual cutting inserts make necessary to attain a very accurate axial positioning of each separate cutting element. Moreover, it is of course necessary that the cutting edges maintain their exact axial positions and do not move dug to the axial forces caused by the contact with the workpiece. Of course, it is also important to obtain a precise radial and tangential positioning of the cutting edge and which positioning also maintain their exactitude, also after a long time of use.
A number of constructions for the precise axial positioning of the cutting inserts and their cutting edges are known per se. However, all of them are marred by one or several disadvantages, such as complicated constructions with many separate parts, or an unsatisfactory axial positioning accuracy. A description of some of these known solutions is now presented underneath.
SE-C-189 159 discloses a milling cutter comprising axially adjustable cassettes which can be positioned by two wedges. The axial positioning is done by pressing the cassette by hand, for instance with the thumb, to the desired position, whereafter it is fixed with the wedges. As can be easily appreciated, no high accuracy is attained. Further, this fixation mechanism comprises at least four separate parts, which complicates the handling.
DE-A-3 530 745 shows a cassette that can be axially positioned in a milling cutter by a differential screw 5. However, also this construction suffers from insufficient axial position accuracy and, moreover, the manufacturing of the cutter body is rendered more difficult by the fact that the cassette recesses do not extend through the whole width of said cutter body. Furthermore, the accessability of the differential screw 5 is obstructed because its head faces axially rearwards and not towards the open and easily accessible envelope surface of the cutter body.
DE-A-3 327 478 also has the inconvenience of the cassette recesses not being through-going. Further, the axial positioning accuracy is not satisfactory because the head of adjustment screw 26 has a too long free extension, which causes an elastic deformation of the screw and a deteriorated position precision of the cutting edge.